1. Field of the Invention
The present invention relates to a diaphragm actuator which corresponds to a kind of hydraulic actuator.
2. Description of the Related Art
Conventionally, there has been known a diaphragm actuator in which a diaphragm 52 is linked in an inner portion of a cup 51 so as to form a pressure chamber 53, a pressure is supplied to the pressure chamber 53 so as to actuate the diaphragm 52 and a rod 54 connected to the diaphragm 52 and the rod 54 is supported by a bearing 55 arranged in an inner side of the cup 51, as shown in FIG. 4. The bearing 55 is mounted to an inner peripheral surface of the cup 51 via a retainer 56, and an outside diameter of the bearing 55 is set to be significantly smaller than an outside diameter of the retainer 56 integrally having a spring receiving portion 56a receiving a spring 57 for returning the diaphragm 52. Further, the bearing 55 is structured such that an inside peripheral surface is formed in a cylindrical shape and an outer peripheral surface is formed in a barrel shape or a circular arc cross sectional shape in which an outside diameter is the largest in a center in an axial direction, so that when the rod 54 swings, the bearing 55 swings within the retainer 56 so as to follow the swing motion of the rod 54.
However, there are the following disadvantages in the diaphragm actuator mentioned above.
That is, since a temperature in an atmosphere in a side of the rod 54 (in a vertically under side of the bracket 57a in the drawing) rises high when the diaphragm actuator is attached to an internal combustion engine or the like in a vehicle via a bracket 57a, a radiation heat is readily transmitted to an internal space 58 of the cup 51 via the metal bracket 57a, a lower surface portion 51a of the cup 51 and a spring receiving portion 56a of the retainer 56, the internal space 58 becomes high in temperature and the diaphragm 52 is exposed to the high temperature. The diaphragm 52 is formed by a rubber-like elastic member having a relatively poor heat resistance. Accordingly, there is a risk that the diaphragm 52 is exposed to the high temperature and thermally deteriorated in shorter time.
Further, in addition, the diaphragm actuator has the following disadvantages.
That is, at first, since the exclusive retainer 56 is provided so as to hold the bearing 55 as mentioned above, the number of parts in the actuator is large. Further, since the bearing 55 is assembled in the retainer 56 at a time of assembling the actuator and an operation of assembling the retainer 56 in the cup 51 is required, an operation of assembling the actuator is complex and troublesome.
Still further, since the diaphragm 52 is structured such that an operating membrane portion 52a and a disc-like center portion 52b held between a diaphragm retainer 59 and a spring retainer 60 are formed in a uniform thickness, and is wholly formed so as to be thin. In addition, an upper end portion of the rod 54 is fixed to a laminated portion comprising the diaphragm 52, the diaphragm retainer 59 and the spring retainer 60 by means of connecting means such as a spin caulking or the like. Accordingly, since a deformation range of a center portion 52b of the diaphragm 52 is set to be small in a manner so as to suitably apply a caulking load to the thin rubber-like elastic diaphragm 52, it is necessary to severely control a magnitude of the caulking load so as to correspond to the caulking condition. Further, since it is a general practice that a pair of upper and lower washers 61 are added to the laminated portion so as to prevent only a caulked portion in the center portion 52b of the diaphragm 52 from being deformed due to the caulking load, there is a disadvantage that the number of parts in the actuator is further increased.
The present invention is made by taking the points mentioned above into consideration, and an object of the present invention is to provide a diaphragm actuator which is excellent in a heat insulation against a temperature in a peripheral atmosphere, thereby preventing a diaphragm from being thermally deteriorated, can decrease the number of parts in an actuator and can make it easy to assemble.
In order to achieve the object mentioned above, in accordance with the present invention, there is provided a diaphragm actuator in which a diaphragm is linked in an inner portion of a cup so as to form a pressure chamber, a pressure is supplied to the pressure chamber so as to actuate the diaphragm and a rod connected to the diaphragm and the rod is supported by a bearing arranged in an inner side of the cup, wherein the bearing is extended to an inner peripheral surface of the cup so as to be brought into contact with the inner peripheral surface, and a contact surface of the bearing with respect to the rod is formed in a circular arc cross-sectional shape having the smallest inside diameter in a center in an axial direction.
In the diaphragm actuator in accordance with the present invention having the structure mentioned above, since the bearing is extended to the inner peripheral surface of the cup and is brought into contact with the inner peripheral surface of the cup, a heat insulating layer against the temperature of the peripheral atmosphere is newly formed by the extended bearing. Since the bearing is made of resin and a heat conductivity of the resin is smaller than that of the metal that is a material of the retainer, it is possible to form a heat insulating layer which can achieve an excellent heat insulating effect.
Further, the bearing is also fixed to the inner side of the cup. Accordingly, the contact surface of the bearing with respect to the rod is formed in the circular arc cross-sectional shape having the smallest inside diameter in the center in the axial direction so as to support the rod in a swinging manner in spite of the fact that the bearing is fixed to the inner side of the cup, and in more detail, the inside diameter in the center in the axial direction is the smallest, the inside diameter is gradually expanded from the center in the axial direction toward both end portions in the axial direction and the cross sectional shape is formed in a smoothly circular arc curved surface.
Further, since the retainer in the prior art mentioned above can be omitted from the constituting elements of the actuator, it is possible to decrease the number of parts and improve an assembling operability.